Monitoring the role of aceticlasts in anaerobic digestion: activity and capacity

Aceticlastic methanogens are seen as a key to digester capacity and stability. This paper develops and applies an assay to measure digester stability by measuring the maximum aceticlastic methane production rate (Vmax,ac). The Vmax,ac in combination with acetate concentrations was found to be an effective digestion monitoring tool to indicate process upsets. At steady state, thermophilic, first stage and short SRT digesters generally had a greater Vmax,ac than mesophilic, second stage or long SRT digesters. The ratio of the Vmax,ac to the plant aceticlastic methane production rate, termed the Acetate Capacity Number (ACN), is a measure of the excess capacity of the digester. Either Vmax,ac or ACN can be used to estimate the capability to handle higher organic loading rates. Monod modeling was used to predict Vmax,ac, ACN and maximum VS loading rates for mesophilic and thermophilic digestion and for staged digesters to better understand expected digestion capacity and stability.